1. Field of Invention
The present invention relates in general to the touch panel technology, and more particularly to the technology of detecting touch points on a touch panel.
2. Related Art
Recently, the applications of touch panels have become wider and wider due to the popularization of electronic products. For example, the touch panels have been used in mobile phones, personal digital assistants and notebook computers to serve as input interfaces. More particularly, the touch panels have further been applied to the typical home appliance products, such as refrigerators, washing machines and the like. Thus, it is obtained that the touch panel technology has become a rapidly grown application in the market.
In the touch panel technology, a resistive touch panel is mostly frequently used. FIG. 1 is a side view showing a conventional resistive touch panel. Referring to FIG. 1, the resistive touch panel includes an upper plate 110, a lower plate 120, and an insulating spacer 130 interposed between the upper plate 110 and the lower plate 120 so that the upper plate 110 is insulated from the lower plate 120 when the touch panel is not pressed. FIG. 2 is a top view showing the conventional resistive touch panel. As shown in FIG. 2, the X-axis and the Y-axis are driven by a pair of voltages ranging from 0 to 5V. When the resistive touch panel is touched by the user's hand or a touch pen, a touch point on the touch panel is pressed to make the upper and lower plates contact with each other. Because the loop on the contact point between the upper and lower plates is turned on, a voltage drop is generated. A controller of the touch panel calculates the ratio of the voltage drop, and then further calculates the coordinate.
However, when two touch points exist on the touch panel, only a voltage drop is generated on the touch panel so that the controller only can calculate the coordinate of one contact point according to the voltage drop. In addition, the coordinate calculated by the controller is also not the coordinate of the actual touch point on the touch panel. In other words, the technology of the conventional resistive touch panel cannot detect multiple touch points on the touch panel.
In addition, U.S. Patent Publication No. US-2008/0129898 A1 discloses the detection technology for the touch panel. FIG. 3 is a system block diagram showing a touch panel disclosed in U.S. Patent Publication No. US-2008/0129898 A1. Referring to FIG. 3, the touch panel has many X-axis sensing lines and many Y-axis sensing lines. In addition, each of the regions, in which the X-axis sensing line and the Y-axis sensing line overlap with each other, has a sensor spacer 92 to which a voltage is applied. The Y-axis sensing lines are respectively coupled to the positive input terminals of the comparators AMP1_1 to AMP1_4, and the X-axis sensing lines are respectively coupled to the positive input terminals of the comparators AMP2_1 to AMP2_5. The negative input terminals of the comparators AMP1_1 to AMP1_4 and AMP2_1 to AMP2_5 are coupled to a reference voltage Vref. When a certain region (e.g., the region A) is pressed, the sensor spacer 92 in the region A makes the X-axis sensing line and the Y-axis sensing line in the region A be short-circuited, and the voltage of the sensor spacer 92 is provided to the X-axis sensing line and the Y-axis sensing line. Therefore, the voltages of the positive input terminals of the comparators AMP1_1 and AMP2_4 are changed so that the voltages outputted from the comparators AMP1_1 and AMP2_4 are changed and the position of the touch point in the region A may be detected.
According to the above-mentioned operation, however, it is obtained that when the regions A and B are simultaneously touched and pressed, the output voltages of the comparators AMP1_1, AMP2_4, AMP1_3 and AMP2_1 are changed. Therefore, the controller of the touch panel may judge that the touch points are in the regions A and B, and may also judge that the touch points are in the regions C and D so that the controller cannot correctly judge the positions of the touch points. Therefore, the above-mentioned touch panel cannot implement the multi-point detection technology due to the restriction of the circuit design.